GSP outstruck Josh 136 to 30 in the fight. In the fourth round, Josh landed ONE of 30 attempted strikes. GSP never looked in danger. He has a way of making good fighters look like amatures. It only takes one mistake to lose (see Matt Sera fight) and he has defended his title, is it 6 times in a row now?
He has beat Josh K x 2, Jon Fitch, Thiago Alves, Matt Hughes, and BJ Penn. I haven't watched all of those fights recently, but what I recall is that he dominated all of those fights. Look at all the different fighting styles from those guys he has beaten, from Division 1 wrestlers, Muay Thai strikers.
When was the last time he lost a round? And as Goldberg always states, how much time has GSP spent on his back (gigidy)? How easily does he take guys down?
Sure, he doesn't finish guys off in flashy manner, but my god, look at Josh Koscheck's face. He got the crap kicked out of him. I don't know, I find it pretty hard to argue that this guy isn't the pound for pound best fighter out there right now. Again, he makes good fighters look ordinary and he never seems to be in danger. I think there's a little more to it than knock outs and the ability to finish. He completely dominates fights, period.
One last quick point, look at the records of the guys you mention, Lidell (defended title 4 times), Shogun (no title defense yet), Rampage (defended title once), Penn (defended title 3 times).